It has been recognized that the use of fixed or pop-up spray heads is advantageous for use in irrigation situations where the available water supply pressure is relatively low or the area to be irrigated is relatively small and irregular in shape. One reason for this is that spray heads are relatively inexpensive to manufacture and maintain, are available in a variety of full and part-circle configurations, operate on water supply pressures typically ranging between about 15 and 30 psi, and produce fan-shaped or full circle-shaped sprays which extend radially outwardly from the spray head over distances between about five and twenty feet, depending upon outlet nozzle size and water pressure.
Further, in recent years, spray heads have been developed to have matched precipitation rates so that the rate of water application produced by a given size full circle spray head is the same as that for the same size part circle spray head operating at the same supply pressure. That is, the spray heads are designed to discharge proportional quantities of water that match the arc or part of a circle they cover so that, for example, a full circle spray head discharges twice the quantity per unit time than that discharged by a half-circle spray head. Similarly a quarter-circle spray head discharges half that of a half-circle spray head.
Matched precipitation rate spray heads are available in both metal (frequently brass) and plastic (frequently molded high strength material such as ABS plastic), and normally are coupled to the outlet of a stationary or pop-up tubular riser. Pressurized water admitted to the riser is projected outwardly by the spray head nozzle outlet as a pressurized, fan-shaped spray that extends radially outwardly and upwardly away from the spray head. Ideally, the water fall-out distribution pattern produced by a spray head, like substantially any irrigation sprinkler, should be a straight line, 30 degree sloped wedge with the maximum precipitation at the spray head and zero precipitation at the maximum radius of water throw. With the ideal distribution pattern, the spacing between adjacent spray heads in an irrigation system should be equal to the maximum radial distance of throw so that the resultant precipitation rate over the area between sprinklers is uniform.
While the use of both metal and plastic spray heads have met with wide acceptance, one problem that has plagued such spray heads is their inability to disburse water in the immediate area around the spray head itself. That is, spray heads have typically produced distribution patterns which have a maximum fall-out commencing approximately two feet radially away from the spray head, and thereafter reducing to zero at the maximum distance of throw. Thus the fall-out distribution pattern of water from both metal and plastic spray heads has generally resulted in little or no appreciable water in the area extending from the spray head radially outwardly to about two feet away, thereby producing an arcuate “dead zone” extending outwardly approximately two feet.
To compensate for this problem, it is common practice in the industry to install the spray heads of a sprinkler system two feet closer together than would otherwise be necessary. While closer spacing does help alleviate the problem of dead zones in the absence of wind, the closer spacing of spray heads results in an increase in the number of spray heads required for a given area, thereby increasing the cost of both material and labor, and total water consumption.
Early attempts to solve the problem of a lack of close-in water from spray head type sprinklers were generally commercially unsuccessful. One early attempt to resolve this problem in part-circle metal spray heads was the addition of a machined, arcuate slit in the body of the spray head below the nozzle outlet. This permits a small portion of the supply water to be disbursed as a low volume, high pressure fan-shaped spray below the main spray. Although the addition of such a machined slit improved the water distribution pattern between three and six feet radially outwardly of the spray head, it generally had little effect on the area between zero and two feet. One reason that the use of an additional machined slit is believed to have been unsuccessful in solving this problem is that the slit must be so small in size that it becomes easily clogged by dirt or rock particles in the water, thereby becoming inoperative.
U.S. Pat. No. 5,642,861 discloses a more recent, but partial solution to the problem. This solution is applicable only to sprinkler heads that produce a partial circle spray pattern. Thus, there remains a need for a full-circle spray head sprinkler having the ability to disburse water to the immediate area between zero and two feet radially outwardly from the spray head in a full circle pattern so as to more closely approximate the ideal distribution pattern.